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diff --git a/doc/html/TechNotes/openmp-hdf5.html b/doc/html/TechNotes/openmp-hdf5.html index decf1de..763d35b 100644 --- a/doc/html/TechNotes/openmp-hdf5.html +++ b/doc/html/TechNotes/openmp-hdf5.html @@ -3,7 +3,8 @@ ---------------------- -I. Introduction to OpenMP +1. Introduction to OpenMP +------------------------- - For shared-memory parallelism - A combination of library and directives @@ -12,34 +13,57 @@ I. Introduction to OpenMP - Information at http://www.openmp.org and http://www.sgi.com/software/openmp -II. Programming(SGI MPISpro compiler and C language) +2. Programming(SGI MPISpro compiler and C language) +--------------------------------------------------- - Turn on compiler '-mp' option - Include 'omp.h' library in program - Use library functions, directives and environment variables -III. Sample Programs +3. Sample Programs +------------------ -Attached are four OpenMP-HDF5 test programs. The purpose of these tests is to -experience OpenMP parallelism with HDF5. All the tests were run on modi4 with -SGI MPISpro compiler(cc) and make. The first two are the working -program. The two following only work occasionally. I modify them directly -from hdf5/examples/h5_write.c. If you want to try them out, the quickest way -is - 1. have your hdf5 program compiled, - 2. go to hdf5/examples directory, - 3. add -mp option to the end of the CFLAGS list in the Makefile. If you +Appendix A contains four OpenMP-HDF5 test programs. (They are derived from +the hdf5/examples/h5_write.c). The purpose of these program is to +test OpenMP parallelism with the HDF5 library. + +All tests were run on modi4 with SGI MPISpro compiler(cc) and make. +Program 1 and Program 2 are the working programs. Program 3 and Program 4 +work occasionally due to racing conditions. +Follow the following steps to try the programs. + + a. have your hdf5 library compiled, + b. go to hdf5/examples directory, + c. add -mp option to the end of the CFLAGS list in the Makefile. If you have the compiled program in another directory, you should go to the examples in that directory. - 4. modify the hdf5/examples/h5_write.c according to the program attached + d. modify the hdf5/examples/h5_write.c according to the program attached here. - 5. use hdf5/tools/h5dump to examine the output file. + e. use hdf5/tools/h5dump to examine the output file. + + +4. Conclusion +------------- + +It is not safe to invoke HDF5 library calls via multiple threads in an +OpenMP program. But if one serializes HDF5 calls as illustrated in Program 1, +the HDF5 library works correctly with the OpenMP programs. + +The serialization of HDF5 calls will slow down the OpenMP program unnecessarily. +Future study is needed to check possible ways to "un-seralize" the HDF5 calls. +One possibility is that the HDF5 library has a beta-version of Thread-safe +implmentation though it is for Pthreads environment. One can check on the +feasibility of running OpenMP programs with this version of HDF5 Thread-safe +library. +======= - I. First Program -------------------------------------------------------------------------------- +Appendix A +------------------------------------------------------------------------- + Program 1 +------------------------------------------------------------------------- /* * This example writes 64 datasets to a HDF5 file, using multiple threads * (OpenMP). Each thread grab the lock while it tries to call HDF5 functions @@ -169,8 +193,9 @@ void CalcWriteData(hid_t fid, hid_t dataspace, hid_t datatype) - II. Second Program -------------------------------------------------------------------------------- +------------------------------------------------------------------------- + Program 2 +------------------------------------------------------------------------- /* * This example compute the element values of an array in parallel * by two threads. Then write this dataset into HDF file. This is @@ -261,8 +286,9 @@ main (void) - III. Third Program -------------------------------------------------------------------------------- +------------------------------------------------------------------------- + Program 3 +------------------------------------------------------------------------- /* * This example create two threads. Each thread writes a dataset to * the HDF5 file in parallel. This program only works occasionally. @@ -356,8 +382,9 @@ void writeData(int id, hid_t file, hid_t dataspace, hid_t datatype, char *dname) } - IV. Fourth Program -------------------------------------------------------------------------------- +------------------------------------------------------------------------- + Program 4 +------------------------------------------------------------------------- /* * This example compute and write two datasets into HDF file in * parallel. It also only works occasionally. @@ -437,6 +464,6 @@ main (void) } --- -Updated: 2000/10/31 +Updated: 2000/11/28 Contact: hdfhelp@ncsa.uiuc.edu </pre> |